1. TECHNICAL FIELD OF THE INVENTION
The present invention falls within the technical sector concerning devices and methods for forming containers for liquid, granular and powder materials, for example for drinks, solid or semi-liquid foods, cleaning products and others.
In particular, the invention relates to a machine and method for forming a container starting from a reel of thermally bondable material in web form, such as polyethylene, polypropylene and all plastic materials, including those bonded to each other and/or to paper or aluminium.
2. PRIOR ART
Devices are known which, starting from one or more shaped flat sheets of material of the so-called bonded type, are able to form a flat walled container, for example of parallelepiped or tetrahedron shape, such as those widely used for containing still drinks.
Devices are also known for forming flat walled containers provided with opening tabs, stoppers or spouts for pouring out the container contents.
The main drawback of known devices is the fact that they can form only flat walled containers generally of parallelepiped shape, and hence very similar to each other, so preventing characterisation and differentiation of the contained product, as instead the industry requires.
A further drawback of known devices is the fact that the flat walls easily deform when internal or external pressures are present, so preventing packaging of products which generate even small pressures, for example moderately sparkling drinks, and leading to undesirable escape of the product from the opened container if gripped too strongly.
The main object of the present invention is to propose a machine and method for forming a container starting from a reel of material in web form which are able to give the container different shapes, including curved walls.
Another object is to propose a machine and method for providing the containers with at least a moderate rigidity to resist at least moderate internal and external pressures.
Another object is to propose a machine and method for forming containers from continuous webs of synthetic materials bonded to aluminium or paper, or from continuous webs of single-layer synthetic materials.
A further object of the present invention is to propose a machine which is of simple construction and maintenance, of high reliability and economically advantageous.
The objects of the invention are attained by a method consisting of folding, and bonding together the edges of, a web unwound from a reel to form a tubular element which is cut into parts of equal length which are mounted over a preferably cylindrical support.
The tubular element is then bonded transversely to its axis to form a closed base, or alternatively a separate base is applied to the end of the tubular element, to hence form an open container.
This latter, still mounted over the respective cylindrical support, is inserted into a mould which is closed about the cylindrical support, and here subjected to internal pressure after heating.
The open container hence assumes the shape of the walls of the mould to which it adheres, and after opening the mould and after suitable cooling it is removed from the tubular support.
According to the invention, the heating temperature is between 30xc2x0 C. and 60xc2x0 C., whereas the cooling temperature is between 5xc2x0 C. and 30xc2x0 C.
The open edge of the container mounted over the cylindrical support can be subjected to an operation for forming a flat flange before its insertion into the mould.
The invention also comprises a machine for forming containers starting from a web wound on a reel, comprising a station in which the web is folded into two, bonded along its facing longitudinal edges and cut into tubular elements of equal length.
An endless conveyor supporting a series of identical cylindrical supports arranged to receive said tubular elements conveys them to the various processing stations.
The first of these is a bonding station arranged to close one end of the tubular element to form a container.
The next station is the forming station in which a mould composed of several mutually movable parts is closed about the cylindrical support to create a sealed chamber; suitable means for heating a compressed gas and feeding it into the container inflate the container to force it against the mould walls from which it assumes its shape.
The mould is then opened and the shaped container withdrawn from the respective cylindrical support.